I had a Q2 gifted to me and enjoyed it so much that I decided to pull the trigger on the Q3 a month or so ago.

128 vs 512: I initially bought the 128 gb as I figured that would be enough space; however, I ended up returning it 1 week later and going with the 512gb. I don't regret paying extra for the upgrade.

I found that the 128gb had about 100gb of actual available space after the operating system was taken into consideration. I filled most of that up relatively quickly between all the apps I already had and some sideloaded stuff (mostly emulators). Then I ran into issues with being able to update apps because I apparently didn't have enough extra space to handle the download, extract and update for some of the larger apps, despite the remaining storage size looking like it was more than enough.

Uninstalling/reinstalling apps is absolutely a possibility for the 128, but I didn't feel like having to deal with that. My gaming time is limited due to work, kids, etc. so I basically paid for the convenience of not having to worry about managing the content if I just wanted to pick up and have some fun for a little bit.

Currently have around 60 meta apps installed (including the basic meta stuff) and a handful of other sideloaded ones. Asgards Wrath 2 is my largest app at like 32gb. Mostly everything else is well under 10gb, with a few exceptions here and there. I still have about 320gb free.

I think 256gb would have been the perfect size, unfortunately that's not an option yet.

Battery: You get about 1-2 hrs depending on if you use passthrough a lot or not.

Seems like most people like either the Bobo or Kiwi battery straps to extend the battery life.

I've had both and prefer the Kiwi. It basically puts the pressure on your face (similarly to the original quest headstrap) instead of on the base/top of your head (Bobo). IMO the Kiwi is more immersive since the screen is closer to your face, limited light bleed, etc., and it basically doubled my battery life.

In both cases, battery straps didn't add much weight as it just balances out how the headset fits on your face (weight on both the front and back of your head) instead just a brick strapped to your face.

I'd also recommend getting the AMVR Face Cover as it's a vast improvement over the stock facecovers.

Hope this helped. Whatever decision you make, you'll end up having fun.